Adhara (Epsilon Canis Majoris)

Adhara (Epsilon Canis Majoris) is the second brightest star in the constellation Canis
Major. It lies below Sirius at the lower
right of a triangle of bright stars known to the Arabs as "the Virgins,"
from which its name (alternatively spelled "Adara" or "Undara") derives.

Adhara is a binary star. The primary
is one of the hottest of the bright stars: so luminous that if placed at
the distance of Sirius (just over 8 light-years), it would shine 15 times
brighter than Venus. Astronomers have used
its spectrum extensively to study the nature of the local interstellar
medium. The secondary, which has an apparent magnitude of +7.5 and an
absolute magnitude of -5.0, lies 7.5" away with a position angle of 161°
of the main star. Yet, despite this relatively large angular separation,
the components can only be resolved in large telescopes, since the main
star is some 250 times brighter than its companion.